Rex,

You wrote just:
Yet they could have had those thing many years earlier, arguably under much better conditions--but didn't, because the Rhodesian Army was so successful that Smith couldn't see the writing on the wall.
At several points in post-UDI Rhodesia, before the war took hold, the senior military commanders did visit Ian Smith, urging him to change his stance in negotiations as Rhodesia was in such a strong position it could make concessions and each time Ian Smith said no there was no need to.

The first time Ian Smith's confidence was punctured was Henry Kissinger's visit in 1976, when a presentation was given by the USA on all aspects of the situation and in particular that the war was not winnable. By that time "taking the gap", falling re-enlistment rates and lack of resources were all having an impact. The Rhodesian military were also astonished that so much had been learnt, much of it from satellite imagery, SIGINT etc.